1. Field of the Invention
The present invention relates to a finder optical system which is independent of a photographing optical system, for example, in a lens shutter camera, and a camera having a finder optical system which is independent of a photographing optical system.
2. Description of the Related Art
A real-image view finder optical system, provided independently from a photographing optical system, has been widely applied to silver-halide-film cameras and digital cameras. The real-image view finder includes a positive powered objective optical system, an image erecting optical system, and a positive powered eyepiece optical system, arranged in that order from the object side, wherein an inverted image formed by the objective optical system is inverted in the vertical and horizontal directions by the image erecting optical system so that an erect image can be viewed through the eyepiece optical system. Such a real-image erecting optical system is, in general, constructed with a Porro prism having a combination of four reflection surfaces.
The Porro prism which has a simple structure, in which an image is inverted by a combination of upper and lower reflection surfaces and right and left reflection surfaces, can be easily machined, and the optical path length of the entire image erecting optical system can be reduced. Therefore, the entire structure of the finder optical system can be simplified.
However, in the Porro prism, the image must be inverted by 180 degrees without overlapping the upper and lower optical paths and the right and left optical paths, and hence, the optical axis of light incident upon the Porro prism and the optical axis of light emitted therefrom is deviated (stepped) in the vertical and horizontal directions by an amount greater than a diameter of the light bundle. The deviation (difference) in the vertical and horizontal directions is always set along the rectangular field of view of the eyepiece optical system in a conventional finder optical system. Consequently, in a finder optical system in which the Porro prism is used for the image erecting optical system, the size in the vertical direction is large, and accordingly, if the finder optical system is incorporated, for example, in a lens shutter camera, the height of the camera is increased.
Moreover, if the Porro prism is used for the image erecting optical system in a real-image type finder optical system, in general, at least the reflection surfaces of the Porro prism are partly located between the image formed by the objective optical system and the eyepiece optical system. In this arrangement in which the image erecting optical system is arranged between the image formed by the objective optical system and the eyepiece optical system, the optical path length between the image and the eyepiece is increased, and hence, it is necessary to increase the focal length of the eyepiece optical system. However, if the focal length of the eyepiece optical system is increased, the finder magnification is reduced. Consequently, the apparent field of view is reduced, thus resulting in difficulty in viewing the finder image or a deteriorated quality of the finder image.
The size of the last surface of the eyepiece optical system (lens diameter) is substantially determined by the apparent field of view and the eye relief. Therefore, as the eye relief is lengthened to provide easy viewing, the eyepiece optical system is made large. In particular, the size of the finder optical system (camera) in the vertical direction is increased.
The present invention provides a finder optical system in which the height of a camera in which the finder optical system is incorporated (length of the minor side of a rectangular field of view of the finder) can be reduced.
The present invention also provides a finder optical system in which the finder magnification and the apparent field of view can be increased and the eye relief can be easily lengthened while reducing the height of a camera in which the finder optical system is incorporated.
The present invention provides a camera having a real-image type finder optical system in which the height of the camera can be made small.
The present invention provides a camera having a finder optical system in which the finder magnification and the apparent field of view can be increased and the eye relief can be easily lengthened while reducing the height of the camera.
The present invention has been completed based on the basic concept that the size of an ocular optical system of a finder optical system is substantially determined by the apparent field of view and the eye relief, whereas there is little restriction to the size of the objective optical system. Hence, the height of an image erecting optical system in the vertical direction can be reduced by arranging one or more of the reflection surfaces constituting a Porro prism that are adapted to invert an image in the vertical direction on the objective optical system side; and the deviation between the optical axis of the objective optical system and the optical axis of the ocular optical system can be reduced by rotating the entire finder optical system about the optical axis of light incident upon the Porro prism without inclining the field frame.
Also, according to the basic concept of the present invention, the camera can be miniaturized by utilizing a substantially triangular space (in which other components are accommodated) between a film winding spool compartment and a photographing lens as viewed from front.
For example, in an embodiment, a finder optical system is provided, including an objective optical system having a positive power; an ocular optical system having a positive power, wherein a light-emitting optical axis of the ocular optical system is parallel with an incident optical axis of the objective optical system, the ocular optical system having a rectangular field of view; a minor direction reflection surface which reflects a light bundle, incident upon the objective optical system, in a substantially minor direction of the rectangular field of view; a first major direction reflection surface which reflects the light bundle, reflected by the minor direction reflection surface, in a substantially major direction, of the rectangular field of view, toward the light-emitting optical axis of the ocular optical system; and a second major direction reflection surface located on the light-emitting optical axis of the ocular optical system to make a connecting optical axis, of the light bundle reflected by the first major direction reflection surface and incident on the second major direction reflection surface, coincident with the light-emitting optical axis of the ocular optical system. The connecting optical axis is inclined with respect to the major direction of the rectangular field of view in a direction in which the incident optical axis of the objective optical system and the light-emitting optical axis of the ocular optical system come close to each other with respect to the minor direction of the rectangular field of view.
It is desirable for the finder optical system to further include a prism provided behind the objective optical system, the prism being provided with the minor direction reflection surface and the first major direction reflection surface.
Three reflection surfaces including the minor direction reflection surface, which reflects the light bundle incident upon the objective optical system in the minor direction of the rectangular field of view, and the major direction reflection surface, which reflects the light reflected by the minor direction reflection surface in the major direction toward the light-emitting optical axis of the ocular optical system, can be located in an optical light path extending from the objective optical system to an image forming position at which an image is formed by the objective optical system.
A field frame which defines the rectangular field of view of the ocular optical system can be provided in an optical light path between the first major direction reflection surface and the second major direction reflection surface.
In another embodiment, a camera is provided, including a photographing optical system, having a substantially rectangular photographic field frame, and a finder optical system which defines a substantially rectangular field of view corresponding to the photographic field frame, the finder optical system including an objective optical system having positive power; an ocular optical system having positive power, wherein a light-emitting optical axis of the ocular optical system is parallel with an incident optical axis of the objective optical system; a vertical direction reflection surface provided on the objective optical system side which reflects a light bundle, incident upon the objective optical system, in the vertical direction of the camera; a first horizontal direction reflection surface which reflects the light bundle, reflected by the vertical direction reflection surface, in the horizontal direction of the camera toward the light-emitting optical axis of the ocular optical system; and a second horizontal direction reflection surface located on the light-emitting optical axis of the ocular optical system to make a connecting optical axis, of the light bundle reflected by the first horizontal direction reflection surface and incident on the second horizontal direction reflection surface, coincident with the light-emitting optical axis of the ocular optical system. The connecting optical axis is inclined with respect to the horizontal direction of the camera in a direction in which the incident optical axis of the objective optical system and the light-emitting optical axis of the ocular optical system come close to each other with respect to the vertical direction of the camera.
The camera can be a silver-halide-film camera which forms an image on silver halide film via the photographing optical system; wherein a camera body of the silver-halide-film camera includes a film cartridge compartment and a film winding spool compartment, a photographing lens having a substantially circular shape with respect to a front elevation and located between the film cartridge compartment and the film winding spool compartment, and a finder optical system provided above the film winding spool compartment. The incident optical axis is located above a substantially triangular space between the film winding spool compartment and the photographing lens, with respect to the front elevation of the camera.
The camera can be a digital camera which forms an image on a solid-state image sensor via the photographing optical system.
The finder optical system can further include a prism provided behind the objective optical system, the prism being provided with the vertical direction reflection surface and the first horizontal direction reflection surface.
Three reflection surfaces including the vertical direction reflection surface, which reflects the light bundle incident upon the objective optical system in the vertical direction of the camera, and the first horizontal direction reflection surface, which reflects the light bundle reflected by the vertical direction reflection surface in the horizontal direction toward the light-emitting optical axis of the ocular optical system, can be located in a light path extending from the objective optical system to an image forming position at which an image is formed by the objective optical system.
It is desirable for a lens of the objective optical system and a lens of the ocular optical system which are externally exposed on the camera body, to each include a rectangular shape defining minor sides and major sides with respect to the vertical direction and the horizontal direction of the camera, respectively.
In another embodiment, a camera is provided, including a photographing optical system having a rectangular photographic field frame having major and minor sides, and a real-image finder optical system for viewing the photographic field frame; the real-image finder optical system including an objective optical system having a positive power; an ocular optical system having a positive power; and an erecting optical system having four reflection surfaces. At least two optical axes, out of three optical axes which are connected to each other via the four reflection surfaces, are inclined with respect to the major and minor sides of the rectangular photographic field frame.
A vertical distance from a point of intersection between a reflection surface provided closest to the object side of the real-image finder optical system and an incident optical axis of the objective optical system, and a point of intersection between a reflection surface closest to an outermost eyepiece lens of the ocular optical system and a light-emitting optical axis of the ocular optical system, can be shorter compared to a case where the at least two optical axes are not inclined with respect to the major and minor sides.
It is desirable for the incident optical axis which is incident on the reflection surface provided closest to the object side of the real-image finder optical system, and the light-emitting optical axis which emits from the reflection surface closest to an outermost eyepiece lens of the ocular optical system, to each extend parallel to the optical axis of the photographing optical system.
The present disclosure relates to subject matter contained in Japanese Patent Application Nos.2001-81622 (filed on Mar. 21, 2001) and 2001-81623 (filed on Mar. 21, 2001) which are expressly incorporated herein by reference in its entirety.